Trigger circuits



. Nov. 13, 1956 Filed Feb. 15, 1954 H. GRAYSON ETAL 2,770,739

TRIGGER cmcurrs 4 Sheets-Sheet J Inventor: H. GRAYSON R. A.G.DUNKLEY A ftorney Nov. 13, 1956 H. GRAYSON ETAL 2,770,739

TRIGGER CIRCUITS Filed Feb. 15, 1954 4 Sheets-Sheet 2 Inventor: H. GRAY SON R. AG. DUNKLEY Attorney 1H? 73,, 1956 H. GRMsoM 'ETAL 2,770,739

TRIGGER CIRCUITS Filed Feb. 15, 1954 4 Shets-Sheet 5 1 K; V W

mm mm 'Y/ Inventors H. G RAY SON R. A.G. DUNK L EY wwwj A Home y Ha GRAYSON TA TRIGGER CIRCUITS 4 Sheets-Sheet 4 Filed Feb. 15, 1954 Inuenlors- H. G RAYS 0N Attorney RAG. DUNKLEY- United States Patent TRIGGER CIRCUITS Harry Grayson and Rowland Arthur George Dunkley, London, England, assignors to International Standard Electric Corporation, New York, N. Y.

Application February 15, 1954, Serial No. 410,394

Claims priority, application Great Britain February 17, 1953 7 Claims. (Cl. 307-88) This invention relates to magnetic trigger circuits. 5

The main feature of the invention comprises a secondharmonic transformer arrangement capable of changeover from one output condition to a second output condition in response to the arrival at an input of an electrical pulse of relatively short duration. 29

The principal object of the invention therefore is to provide a trigger circuit which depends for its trigger action on a second-harmonic transformer.

Another object is to provide a pulse counting chain incorporating trigger circuits comprising second-harmonic transformers.

The invention will be described with reference to the accompanying drawings in which:

Fig. 1 shows a bi-stable trigger circuit;

Fig. 2 is a simplified representation of the circuit of Fig. 1;

Fig. 3 shows schematically a counter employing trigger circuits of the type shown in Figs. 1 and 2;

Fig. 4 shows three waveforms occurring in the circuit of Fig. 3;

Fig. 5 shows in detail a part of the circuit shown schematically in Fig. 3;

Fig. 6 shows in detail another part of the circuit shown schematically in Fig. 3;

Fig. 7 shows a second form of bi-stable trigger circuit and Fig. 8 shows a binary counting circuit employing the trigger circuit of Fig. 7.

Referring to Fig. 1, a bi-stable magnetic trigger circuit comprises basically a second harmonic transformer. This transformer may conveniently be of the construction described in the application, Serial No. 410,387, filed February 15, 1954. According to this construction the transformer comprises two annular cores 5 and 6 of rectangular cross-section formed from tape of a saturable magnetic material and constituting a three-limbed core. Two primary coils a, a are wound in the same sense on the outer limbs 7 and 9 of this core. They are connected in series to a source A of alternating current of carrier frquency, for instance 50 kc./ s.

Two secondary coils ,8 and 'y are wound on the common limb 8 of the three-limbed core. Since the primary coils a, a are wound in the same sense the magnetic fluxes through the common member 8 of the three-limbed core, due respectively to the coils a and a will be opposed. Accordingly when alternating current flows in the primary windings or, 0: there would ideally be no current induced in the secondary windings .B and 'y. However, it is well known that if a direct current flux is superimposed upon the alternating .flux,..then even harmonics, predominately the second, of the alternating current frequency appear in the secondary windings.

One stable state of the device of Fig. 1 is therefore that in which only alternating flux is generated in the core-members, and that due to the alternatingcurrent applied at A. However, it is impossible to construct a 2,770,739 Patented Nov. 13, 1956 device in which the two primary coils a, m are perfectly balanced. There will therefore always be at least a lowlevel second harmonic frequency generated in the coils ,B and '7. To prevent this signal being rectified the rectifier r1 must be blocked. To this end a small positive standing bias potential (which will usually need to be of the order of 10 volts) is applied at the terminal G. The circuit then behaves effectively as if there were no induced current in the secondary windings. This will be referred to as the off state.

To switch the trigger circuit into the on state a positive potential greater than the standing bias at terminal G is applied momentarily at the terminal K. A pulse of current flows through the inductance L and the secondary winding 7 to G.

If desired the y-winding may be shunted. by a resistance R2 and a neon lamp N to indicate when the 'y-winding is energised. This indicating circuit has been shown in the drawing but is of course optional.

Th current pulse in the y-winding causes unbalance of the flux in the two cores and the level of the secondharmonic signal in the IB-Winding rises sufficiently to allow the rectifier r1 to conduct. Thus, even though the original current pulse caused by the application of a positive potential to the terminal K has by now decayed, direct current rectified by the rectifier r1 will energise the -winding via the inductance L This direct current will in turn caus the generation of a higher level of second-harmonic in the ,B-winding. Thus by a cumulative process the other stable state, which will be referred to as on is established. This will be indicated by the discharge of the neon lamp N.

To return the circuit to its off condition it is merely necessary to interrupt the carrier supply instantaneously. The second-harmonic in the fi-winding will disappear completely. No rectified current will then be fed back to the 'y-winding to sustain the direct current bias so that when the alternating current supply is re-established in the primary windings cc, 06 only the low-level secondharmonic caused by unbalance appears. The rectifier is therefore blocked once again. The circuit could be made responsive to a negative triggering pulse applied at K simply by reversing the poling of the rectifier n.

In th remaining circuits to be described simplified circuit diagrams will be used. The simplications introduced will be explained with reference to Fig. 2. This drawing shows the simplified diagram of a trigger circuit identical with that of Fig. 1. In this diagram neither the cores 5 and 6 of saturable magnetic material nor the primary windings a, a have been shown. However it is to be understood that both these elements are present and moreover, that the primary windings are energised from a source of alternating current of carrier frequency. By omitting the cores from the diagram it becomes possible to draw the secondary windings t and in any con venient position relative to the remaining circuitry.

The arrangement of a number of magnetic triggercircuits to form a counter for pulses will now be described The basic principles of operation of the counter will first be described with reference to the block diagram of Fig. 3. In this diagram a frequency doubler DL and a doubler-inverter circuit DLI are both fed with alternating current of carrier frequency, say, at the inputs F and H respectively. Due to the second-harmonic amplifier effect alternating currents of frequency 2. are generated in the circuits DL and DLI. The input for the pulse-train to be counted is at P.

The circuits DL and DLI will later be described in greater detail with reference to Fig. 5. It is sufiicient at this point to remark that a second-harmonic signal of frequency 2 is transmitted by the doubler circuit DL 3 only during the existence of a pulse of potential at the input P. On the other hand the doubler-inverter circuit transmits a second-harmonic signal only when there is no pulse at P. Referring to Fig. 4, the wave-form represents the pulse train to be counted which arrives at the input P. The waveform a is to output wave-form from the doubler circuit DL, and, has a pulse of alternating current corresponding to each pulse of the waveform 0. The wave-form b represents the output from the doubler-inverter DLI. In this case a pulse of alternating current corresponds to the quiescent periods of the pulse-train to be counted, the waveform b being itself quiescent during each occurrence of a pulse at the input P. In the diagrams of the pulse trains a and b the rectangular outlines are of course merely diagrammatic, having been inserted to delineate the pulses.

Referring again to Fig. 3 the elements la, lb, 2a, 2b are four of a number of trigger circuits of a type similar to that described with reference to Figs. 1 and 2. Suppose now that some starting signal is applied to the circuit 1a during the application of a pulse of potential to the input P, then that circuit will go into its on condition. This condition will persist until the decay of the pulse applied at P. As long as the circuit 1a is on, an output is delivered to the next circuit 1b. An arrangement is provided whereby this output persists for a short time after the decay of the input pulse at P. As soon as this input pulse has decayed, a pulse of alternating current of the waveform b (Fig. 4) is applied to the circuit 1b which thus goes on. This condition persists until the decay of the pulse P causes DLI to go off and DL to come on at which point 2a is triggered on. In this way counting proceeds down the chain. There will always be one trigger circuit of the chain in its on condition. During the counting of a pulse that trigger circuit will be one of the a series while during the quiescent state of the input pulse-train the active trigger circuit will be one of the b series. To make a cyclic counter counting by n it is merely necessary to arrange for the nb element to trigger the la element.

The operation of the counter will now be described in detail with reference to Figs. 5 and 6 which show circuits simplified in the manner previously described. Since the doubler and doubler-inverter circuits DL and DLI are required to deliver current to a large number of trigger circuits they are required to deliver more power than the individual trigger circuits and so must usually be larger. In one practical case each switch had two annular cores each consisting of approximately 10 ft. of Permalloy C tape wide and .001 inch thick. The primary windings were divided as before, a half on each core. However, it was found to be convenient to arrange the secondaries also in two halves, one on each core instead of placing the two cores in close physical relationship in order to constitute a common limb as previously.

Referring now to the upper part of Fig. 5 which shows the doubler circuit DL, the secondary windings each comprise two parts 131, B1 and 'y1, v1 The primary winding a1, ai (not shown) is fed from a source of alternating current of frequency f. The coils 0:1, 131 and Y1 are all wound on one of the annular core-members described above, and the coils 1x1 [31 and 71 on the other. As indicated in the diagram, the coils [31 and [31 are opposed and 71 and 1 are opposed so that the fundamental frequency f and even harmonics thereof do not appear in the secondary windings.

The cores of the doubler inverter circuit DLI likewise each carry a part of the primary winding :12, e2 (not shown). These are also fed from a source of alternating current which is usually, but not necessarily of the same frequency f as that feeding the winding :11, 111 of DL. The cores of DLI each carry three secondary windings 32, 132 and v2, 72 and 73, 'ys The two parts of each of these secondary windings are opposed so that the fundamental frequency and odd harmonics thereof do not appear in them. In addition the two-windings are wound so as to produce fluxes in opposite directions in each of the annular cores.

When there is no pulse of potential at the pulse input P, the rectifier D is blocked by the potential of the battery E. At the same time direct current flows to earth via the 'ya-windings and the resistance R3. The resultant direct current flux, superimposed upon the existing alternating current flux causes even harmonics, predominantly the second, of the fundamental frequency f to appear in the secondary windings. The values of L and C in the circuits Q2 "and Q3 are so chosen that those circuits tune to the second harmonic frequency 2]; this frequency does not then leak into the remainder of the circuit. The second harmonic appearing in the ,B-winding is fed at Y to the b-stages of the counting chain.

The potential of the battery E is so chosen that when a pulse of the pulse-train to be counted (0 of Fig. 4) matures at P, the rectifier D conducts. This rectifier nevertheless ensures that the points S and T :are held at equal potentials. Equal currents therefore flow through the secondary windings 72 and 73 to earth.

It has already been explained that these two windings are in opposition on each of the core-members. Accordingly no direct current flux is generated in either coremember. Any residual unbalance may be adjusted by means of the variable resistance R2. In the absence of any direct current flux even harmonics are not induced in the secondary windings so there is no output at Y.

Meanwhile the existence of a positive pulse at P causes a direct current to flow to earth over the winding '71, 'y1 of DL. Accordingly a second harmonic output appears at X where it is fed to the a stages of the counting-train. The circuit Q1 is tuned to the second harmonic frequency 2 so that this does not appear in the remainder of the circuit.

Referring now to Fig. 6 the counting-train comprises n identical at stages, and n identical b stages. The a and b stages are similar to the circuits of Figs. 1 and 2 and differ from one another only in the poling of the rectifiers Da. and Db and the connection of the -y-winding. In each of the a stages the 'y-winding is connected between the choke L--L and a point N which is biassed to a small negative voltage, whereas in the b stages the connection is between the choke and earth. The negative bias at N must, as previously described, be suflicient to block the rectifier Da so as to prevent rectification of the low-level second harmonic signal which appears in the fi-winding when the stage is off due to unbalance in the primary windings a. In addition to blocking the rectifier Da, the negative bias at N of stage 111 also blocks the rectifier Db of stage nb. Similarly the rectifier Db of the stage 1b is blocked by the negative bias at N of stage 2a.

The primary winding 0:, a (not shown) of each of the a stages is connected to the terminals X of Fig. 5, while the primary winding of each of the b stages is connected to the terminals Y of Fig. 5

Consider now the arrival of a pulse of the pulse-train to be counted (0 of Fig. 4) at the input P (Fig. 5). A corresponding pulse of carrier appears at X and is applied to the primary windings of all a stages. During the duration of this pulse the potential of the point N is lowered beyond its normal biassing values. This produces an effective current in the 'y-winding. A significant level of the second harmonic frequency (4 appears in the winding 19, the rectifier is no longer blocked and by the cumulative process described earlier the on condition of this first stage is stabilised.

Meanwhile direct current flows through the -winding of stage 1b which does not of course come on since there isno carrier applied to its primary windings.

When the pulse applied at P decays the carrier supply to the 4 stages ceases. However the condenser C and the resistance R of stage 1a together with the inductance L of stage 111 produce sufficient delay to ensure that the current through the winding of stages 112 does not decay completely before the circuit DLI produces a second harmonic output to be fed to the b stages.

Transfer stage 2a occurs in an analogous fashion when the next pulse matures at P. The counting continues in this way until the arrival of the (n+l)th pulse causes the nb stage to trigger the In stage into its on condition once more, the cycle then being complete.

' In order to give an output for registration purposes an auxiliary fl-winding is wound on the core of each of the a stages. The auxiliary winding of the stage 1a is shown at B1 in Fig. 6. Now, it will be remembered that the on stage of the stage 1a is characterised by an appreciable current in the ,8 winding. This current will induce a current in the auxiliary winding 81 which is then used to operate a suitable registering device M1. Each of the a stages is provided with such a registering circuit so that the arrival of each pulse at the input P(Fig. 5) is registered. 1

In the case of a counter counting by ten, for instance, the tenth stage completes the cycle by triggering the first stage and in addition may be arranged to trigger the first stage of a decimal counted. The decimal counter then advances one stage for the completion of every cycle of the unit counter.

Referring to Fig. 7 another form of bi-stable circuit comprises two secondharmonic magnetic amplifiers. The circuit .is in its simplified form, the annular cores and the primary windings not being shown. The primary windings are of course wound in such a way that the fundamental frequency applied to the primary windings and odd harmonics thereof, do not appear in the corresponding secondary windings.

Equal positive potentials are applied at J 1 and J2. Similar direct current paths exist from each of these sources of potential to earth. In the case of the potential-source I1, the path is over 71, the -y-Winding of the first magnetic amplifier, the inductance L2, the rectifier D2 and the resistance R2. In the case of the potential-source J2 the path is over 72, the -winding of the second magnetic "amplifier, the inductance L1, the rectifier D1 and resistance R1. The current flowing in each 'y-winding will cause the second harmonic of the carrier frequency to appear in the ,B-windings. These induced currents will be rectified by the rectifiers 1-1 and r2. The rectified currents will raise the potentials of the points U and V to values above those of the potentials applied at I2 and I1 respectively. There will thus be a tendency for the rectifiers D1 and D2 to be biassed so as to prevent the flow of direct current through the corresponding -windings v2 and 71 However, though the values of corresponding components on the two sides of the circuit are substantially equal there will .in practice he variations which will cause the current through one of the 'y-windings, 7 for instance, to be greater than that through the other. Thus upon switching on the carrier supplies and applying bias to the terminals J1 and J2 the circuit will be stabilized with amplifier 1 on and amplifier 2 off, (i. e. current flowing in *yr and D1 blocked). The condition of the circuit can be reversed by arranging for a current to flow momentarily in the winding v2. The resulting pulse of second-harmonic frequency in the winding 52 raises the potential of the point V and so biases the rectifier D to prevent direct current flowing through the winding '71 to earth. The change is then cumulative until the circuit becomes established in its second stable state with the first transformer o and the second on.

Fig. 8 shows how the bi-stable circuit of Fig. 7 may be adapted to count narrow positive pulses of potential of amplitude approximately equal to the potential applied at the points J1 and J2. The circuit differs from that of Fig. 7 in that the potentials applied at J1 and J2 are fed to the -windings 'yl and 72 over resistances R1 and R2 respectively, each shunted by a condenser, C1 and C2 respectively.

The pulses to be counted are applied at the terminal P and are fed to the points U and V through rectifiers rs and r4.

Suppose that upon switching-on the carrier and direct current bias supplies that circuit stabilises with first transformer on and the second ofi. The winding 1 will be passing current and there will therefore be a potential gradient over the resistance R1 Accordingly the condenser C1 will be charged.

As in the circuit of Fig. 7, the second harmonic of the carrier frequency will be induced in the winding ;81. This alternating current will be rectified at r1 and will raise the potential of the point U to a value sutficient to block the rectifier D1. No current can then flow through R2 and 72 and the condenser C2 will not receive any charge.

Upon the arrival at P of the leading edge of a pulse of potential of amplitude approximately equal to the potential applied at Jr the rectifier D2 will also become blocked. The current in winding 71 will cease and in consequence no further second harmonic current will be induced in B1 and the potential of the point U will fall to that of the top of the pulse. Nevertheless the rectifier D1 is still biased sufficiently to prevent current flowing from I2 to earth. Meanwhile the condenser C1 begins to discharge.

It is essential that the time-constant of the network R1 C1 is such as to ensure that the condenser does not discharge completely before the decay of the pulse being counted. At the trailing edge of the pulse the rectifiers D1 and D2 are both momentarily conductive. However the effect of the discharge current of the condenser C1 'is to reduce the total current flowing through the 'yl-Wlllding. The current through this winding is therefore less than that through the z-winding. In consequence, a higher level of second harmonic current is induced in the ,Bz-winding than in the [ii-winding and the blocking of the rectifier D2 will be more effective than the blocking of the rectifier D1. By the usual cumulative effect the second transformer comes on while the first is driven off. The condition of the circuit has therefore been reversed by the application of a pulse at P.

The .choice of the biassing potential applied at J1 and J2 will of course depend upon the amplitude of the pulses counted, while the values of the resistances R1 and R2 and the condensers C1 and C2 will be determined by the pulse-width.

The circuit may be readily adapted to count negative pulses by reversing the poling of each of the rectifiers and biasing J1 and 12 negative instead of positive.

Although the invention has been described with reference to an embodiment employing second-harmonic transformers constructed according to the method described in the application referred to above, other second harmonic transformer devices could of course equally well be employed.

While the principles of the invention have been described above in connection with specific embodiments, and particular modifications thereof, it is to be clearly understood that this description is made only by way of example and not as a limitation 011 the scope of the invention.

What we claim is:

l. A trigger circuit comprising a single second-harmonic transformer having a primary winding and first and second secondary windings, a first input connected to said primary winding and adapted to have alternating current applied thereto, a second input connected to said first secondary Winding and adapted to have pulses of relatively short duration applied thereto, an output connected to said second secondary winding, said second secondary winding adapted to provide a path for an alternating current of a frequency which is an harmonic derivative of said alternating current applied to said first input, a feedback circuittconnected from said second secondary winda, ing to said first secondary winding for passing current therebetween the: produce a condition of sustained output,. and" means for interrupting said alternating current in said primary winding to produce a condition of no output.

2. A magnetic counting circuit comprising a counting input circuit adapted to receive electrical pulses. of relatively short duration to be counted, a first plurality of second-harmonic transformer arrangements, a second plurality of second-harmonic transformer arrangements, each of said second-harmonic transformer arrangements, comprising a single second-harmonic transformer having a primary winding and first and second secondary windings, a first input connected to said primary winding and adapted to have alternating current applied thereto, a second input connected to said first secondary winding and adaptedtto have pulseseof relatively short duration applied thereto, an output connected to said second secondary winding, saidsecond secondary winding adapted to provide a path for an alternating current of a frequency which is an harmonic derivative of said alternating current applied to said first input, a feed-back circuit connected from said second secondary winding to said first secondary winding for passing current therebetween to produce a condition of sustainedoutput, and meanstfor rectifying current in said output, means for applying an alternating'current to the first input of each of said first plurality of second-harmonic transformer arrangements in response to the arrival ofa pulse to be counted at said counting input, means for applying an alternating current to the first input'of each of said second plurality of second-harmonic transformers when there is no pulse at said counting'input, and means forapplying the rectified current inthe output of each of said second-harmonic transformer arrangements to the second inputs of respective transformer arrangements of the other plurality of transformer arrangements, the order of transfer being from the first arrangement of the first plurality to the first arrangement of the second plurality, from the first arrangement of the second plurality to the second arrangement of the first plurality, and so on, whereby the arrival of pulses at'said counting input is represented by a: sustained output from successive transformer arrangements of said first plurality.

3. A magnetic counting circuit, as claimed in claim 2, in which means are provided for applying the output of the last one of said second plurality of second-harmonicv transformer arrangements to the second input of the first one of said first plurality of second-harmonic transformer arrangements.

4. Atbistable trigger *cihcuit: comprisingfirstland; second single'. second-harmonic. transformers eachthaving a primary winding and first and second secondary windings, a first input connected to said primary windjngand adapt-- ed tovhave alternating current applied thereto a second input connected tozsaid first secondary windingiandadapted to have pulses ofrelatively, short duration applied thereto,- an output connected to said second secondary. winding, said second secondary winding, adapted to pro-- vide a path for an alternating current of a, frequency which is an harmonic derivative'of said alt'ernating,current applied to said-first input, a feed-back circuit connected from said second secondary winding to said first secondary winding for passing current therebetween to produce a' condition of sustained output, means' for caus ing current in the output of saidfirst second-harmonic transformer to prevent current from flowing in the sec ond input of said second-harmonic transformer, and

means for causing current in the output of said second" second-harmonic transformer to prevent current from flowing in the second input of said first second-harmonic transformer.

5. A bistable trigger circuit, as claimed in claim 4, in which the means to prevent a current flowing in thein-v puts of the first and second transformerscomprises in sponsive to thearrival of a pulse atsaidsingle 'pulse input' for driving each of said transformersinto a-condition of no output, and in which eachzof said transformers is providedtwith electrical storage meansconnected to the second input, whereby the one of said transformers which was initially in a.condition ofsustainedoutput is inhibited from returningv to that. state by the charge stored.

by the associated storage-means.

7. A binary countingrcircuiavas claimed in claim. 6,-

in which said electrical storage means are condensers,

References Cited'in the file of this patent UNITED STATES PATENTS 2,519,513 Thompson Aug; 22, 1950 2,640,164 Gill et al May 26,1953 2,652,501 Wilson Sept; 15, 1953 2,654,080 Browne Sept; 29, 1953. 

